Explanation of Surface-Enhanced Raman Scattering Intensities of <i>p</i>-Aminobenzenethiol by Density Functional Computations

Abstract

p -Aminobenzenethiol (ABT) is a popular molecule for surface-enhanced Raman scattering experiments (SERS), providing large signal enhancements on a range of metal surfaces. However, SERS intensities vary very much according to experimental conditions, and the interplay between ABT protonation, polymer state, and electronic structure/Raman cross section is still not completely clear. To understand main factors affecting Raman intensities, density functional theory (DFT) and matrix polarization theory (MPT) models were used to generate the spectra and compare to the experiment. The simulations showed that ABT protonation as well as its binding to the metal surface shift the absorption threshold, which invokes resonance or preresonance conditions favorable to the signal enhancement. The MPT approximation enabled modeling of the effect of the metal bulk and orientation of the dye on the metal surface on the enhancement and relative band intensities. The simulations can be done relatively easily and reveal chemical changes and system geometry important in rational design of SERS molecular sensors.